1.Field of the Invention
This invention relates to a photosensitive recording material with reduced pressure sensitivity.
2.Description of Related Art
During manufacture, storage, and processing, photosensitive silver halide recording materials are moved while in contact with surfaces of, for example, other films, guide rollers, and metal plates in exposure devices, cassettes, and development machines. Such surfaces have irregularities or peaks due to dirt, dust, scratches, or matte agents. The tips of such peaks exert considerable pressure on the material's surface, a pressure that is transferred to the silver halide grains and that can lead to pressure sensitization. Developing the materials blackens these contact sites even if not exposed, producing gray or black pressure marks. This occurs even if the outer layer has not been damaged mechanically. The pressure marks are usually black lines, that degrade the recorded image. Such black pressure marks are especially disadvantageous in phototypesetting film and in films that are processed by infectious development.
The problem of pressure sensitivity has assumed greater significance with the trend to more rapid and largely automatic handling of the materials, for example, during exposure. The problem cannot be solved by simply increasing the binder in the emulsion or the thickness of the protective coating, because of concurrent requirements for rapid processing.
Patent Application EP 02 09 010-A2 describes recording materials with ultrahigh contrast and reduced pressure sensitivity and containing polyhydroxybenzenes, for example, hydroquinone. However, the pressure sensitivity of these materials drops only after long storage, and photosensitivity decreases simultaneously.
Patent Application EP 04 90 302-A2 proposes adding silica to the emulsion layer and limiting the coefficient of friction by incorporating a slip agent in the protective layer.
Incorporating soft polymer latexes in the emulsion layer or in the top layer is also known to reduce pressure sensitivity (see, for example, Research Disclosure 308 119, December 1989).
The known methods do indeed yield a certain reduction in pressure sensitivity, but a reduction which, in many cases, is inadequate. Furthermore, slip agents or latexes incorporated in the coatings, especially in larger quantities, produce an array of other disadvantages, such as tackiness, reduced scratch resistance, haze, and the need for longer processing times. Colloidal silica damages the planarity of the material and increases the viscosity of coating solutions in an undesirable manner.
The problem involved in the invention is to make a rapidly processible, photosensitive silver halide recording material that is largely insensitive to the occurrence of pressure marks and has low haze and optimum sensitometric properties.